\begin{tikzpicture}
    \tkzDefPoints{0/0/A, 3/0/B, 1/2/C}
    \tkzDefPointBy[projection=onto A--B](C)  \tkzGetPoint{H}
    \tkzDefPointBy[translation=from A to B](C)  \tkzGetPoint{D}

    \tkzDrawPolygon(A,B,C)
    \tkzDrawSegments(C,H)
    \tkzDrawSegments[dashed](B,D  C,D)
    \tkzLabelPoints[above](C,D)
    \tkzLabelPoints[below](A,B,H)
\end{tikzpicture}

